I will not run any .exe files except for Steam itself. I will use Wine just to play Steam games. But I'm affraid WIne is an open door for network attacks, something like a friend getting my IP and trying to invade my machine

Wine doesn't open any doors on your computer, if someones attacks you is probably a security issue on steam rather than wine (most probably)..Anyway any kind of software you run can be a potential security issue if some kind of a exploitable bug is found...

WINE itself doesn't open any doors and applications run by WINE has no root access. Tbh as long as you do not use WINE for pirated apps it will be fine and if you think that WINE behavior is suspicious (or specific app), you can always kill the process easly, which very often is not possible under Windows. Also you can remove all links from WINE prefix to your HOME folder to improve the feeling of being secure (there is an option in WINETRICKS for that) :)

I'm not sure if you're labouring under some sort of misconception, but the Windows version of Steam is 'steam.exe'

Given that you have a working Linux Steam install, why would you want to install the Windows version under WINE (or PlaysOnLinux) if you don't actually intend to install any games?

As towo01 pointed out any game is an executable. If you have installed any games via Steam under WINE, all that Steam does is provider a launcher for the executable i.e. You run an executable for the game if you launch it from Steam - this is true regardless of platform.

As to security with WINE - if you'd be happy running a game from steam under Windows, you should be happy running it under WINE.

I'm not sure if you're labouring under some sort of misconception, but the Windows version of Steam is 'steam.exe'

Given that you have a working Linux Steam install, why would you want to install the Windows version under WINE (or PlaysOnLinux) if you don't actually intend to install any games?

As towo01 pointed out any game is an executable. If you have installed any games via Steam under WINE, all that Steam does is provider a launcher for the executable i.e. You run an executable for the game if you launch it from Steam - this is true regardless of platform.

As to security with WINE - if you'd be happy running a game from steam under Windows, you should be happy running it under WINE.

Wine doesnt have a proper 'system32' or the whole windows bundle with it, so all in all anything that targets windows(malware i mean) should -not- work with it. But thats relative to an extent.I would roughly say wine is safer than windows, it runs on linux you know.